A few quotes from Peopleware
on the subject of overtime:
Overtime for salaried workers is a figment of the naive manager's imagination.
Oh, there might be some benefit in a few extra hours worked on Saturday to
meet a Monday deadline, but that's almost always followed by an equal period
of compensatory "undertime" while the workers catch up with their lives.
Overtime is like sprinting: It makes some sense for the last hundred yards
of the marathon for those with any energy left, but if you start sprinting
in the first mile, you're just wasting time.
It has been our experience that the positive potential of working extra hours
is far exaggerated, and that its negative impact is almost never considered.
That negative impact can be substantial: error, burnout, accelerated turnover,
and compensatory "undertime" ... When you take into account the way that the
team members' differing abilities to work overtime tends to destroy teams,
the case against it becomes persuasive.
They further note that Jerry Weinberg
proposed an interesting psychological
explanation for why so many folks propose overtime even though they know
it's not going to help: "we don't work overtime so much
to get the work done on time as to shield ourselves from blame when
the work inevitably doesn't get done on time".